The present invention relates to a rotary damper for dampening the relative rotation between a driven rotary member and a stationary support member, which rotatably supports said driven rotary member, with the viscous resistance of a viscous fluid.
As an example of the aforementioned rotary member, a damper comprising the following is known: a driven rotary member, which integrally includes a driven rotary part that engages with a driving member, such as a gear and rack; a stationary support member, which rotatably holds said driven rotary member; an annular housing, which is formed between said stationary support member and driven rotary member; a sealing means, which seals the outer peripheral edge of said housing so as to allow the driven rotary member and the stationary support member to relatively rotate; and a viscous fluid, which is stored in the housing and dampens the relative rotation of the driven rotary member and the stationary support member.
Patent Reference 1: Japanese Utility Model No. 2603574.
In the conventional rotary damper described above, an opening (orifice) is provided in the center of the stationary support member to provide communication between the housing and the atmosphere to thereby prevent the unnecessary (more than necessary) air from remaining within the housing during assembly of the driven rotary member and the stationary support member to facilitate the assembly, and prevent the air from mixing in with the viscous fluid to maintain a constant torque level. The rotary damper, however, includes no measures to prevent the viscous fluid from leaking from the opening (orifice), i.e., the opening (orifice) is not closed. Thus, the viscous fluid occasionally leaks from the opening (orifice) when used under a high temperature. Several rotary dampers wherein the leaking of viscous fluid from the opening (orifice) has been taken into consideration and thus include no opening (orifice) to provide communication between the housing and the atmosphere have been proposed.
Patent Reference 2: Japanese Utility Model Publication (Kokoku) No. 01-37236
Patent Reference 3: Japanese Patent No. 3421484
Patent Reference 4: Japanese Utility Model No. 2519149
Patent Reference 5: Japanese Patent Publication (Kokai) No. 11-30261
Providing no opening (orifice) for the housing to communicate with the atmosphere, however, traps air in the housing and makes the assembly more difficult. It also allows the air to mix in with the viscous fluid and causes torque level variations or instability in torque accuracy (irregular torque levels).
The present invention has been made in order to eliminate the inconveniences described above, and provides a rotary damper that eliminates the entrapment of unnecessary air in the housing, thereby facilitating assembly and preventing air from mixing with the viscous fluid for the maintenance of a precise torque level.
Further objects and advantages of the invention will be apparent from the following description of the invention.